The present invention is directed to bicycle transmission devices and, more particularly, to a bicycle derailleur with rotation resistance.
A typical bicycle derailleur transmission includes a plurality of sprockets that rotate together with a front crank or with a rear wheel, a chain, and a derailleur that selectively shifts the chain among the plurality of sprockets. A typical derailleur includes a base member adapted to be mounted to the bicycle frame, a movable member movably coupled to the base member, and a chain guide coupled to the movable member. The chain guide engages the chain to selectively switch the chain among the plurality of sprockets when the movable member moves relative to the base member.
The chain guide of a rear derailleur ordinarily is rotatably mounted to the movable member and is spring-biased in a clockwise direction so that the chain guide can take up the slack in the chain when the chain engages the smaller-diameter sprockets. However, during rough riding, bumps and shocks may cause the chain guide to rotate counterclockwise, thereby creating undesirable slack in the chain. To prevent this from occurring, motion resisting structures have been added to some rear derailleurs. An example of a motion resisting structure is disclosed in U.S. Patent Application Publication Number 2009/0054183 A1. As shown therein, a bicycle derailleur comprises a base member adapted to be mounted to a bicycle, a movable member movably coupled to the base member, and a chain guide coupled to the movable member. The chain guide is coupled for rotation around a rotational axis, and a biasing element biases the chain guide in a selected rotational direction around the rotational axis. A resistance-applying unit applies a resistance to rotational movement of the chain guide in a direction opposite the selected rotational direction, and an adjusting unit adjusts an amount of resistance applied by the resistance-applying unit.